Hi alexismalin05,
If you're unable to send or receive messages, please check out this link, which can help resolve some Messages issues: If you can't send or receive messages on your iPhone or iPad
Just to clarify, are you also being prompted to add your phone number for Messages? If so, please check out this link, which explains how to do that, and will guide you through that process: Add or remove your phone number in Messages or FaceTime
Set up your phone number
On your iPhone:
1. Go to Settings > Messages and make sure that iMessage is on. You might need to wait a moment for it to activate.
2. Tap Send & Receive. If you see "Use your Apple ID for iMessage," tap it and sign in with the same Apple ID that you use on your Mac, iPad, and iPod touch.

3. In the "You can receive iMessages to and Reply From" section, make sure that your phone number and Apple ID are selected.
4. Go to Settings > FaceTime and make sure that your phone number and Apple ID are selected in the "You can be reached by FaceTime at" section.
On your other devices, you can now turn on the phone number that you just set up:
* Turn on your phone number for your Mac
* Turn on your phone number for your iPad or iPod touch
Thanks!